NASA's Magnetospheric Multiscale (MMS) mission investigates how the Sun’s and Earth’s magnetic fields connect and disconnect, explosively transferring energy from one to the other in a process that is important at the Sun, other planets, and everywhere in the universe, known as magnetic reconnection. Reconnection limits the performance of fusion reactors and is the final governor of geospace weather that affects modern technological systems such as telecommunications networks, GPS navigation, and electrical power grids. Four identically instrumented spacecraft measure plasmas, fields, and particles in a near-equatorial orbit that will frequently encounter reconnection in action.